A bit plane is a horizontal slice through the data, collecting the values of a given bit position from all of the data values in the set. For example, consider an array filled with 1000 elements of 16-bit data. This array can be divided this into 16 1000-bit arrays, the first of which would have all of bits for bit-position 0, the next would have all of the bits for bit-position 1, etc. Each of these 16 1000-bit arrays is a bit plane.
The invention is embodied in a code sequence that converts a sequence of N bit numbers and produces a set of N bitmaps. The N bits of each number are generally stored together in a single storage unit such as a single memory location. Each bitmap contains one bit plane from the original data set.
This invention effectively converts N-bit data (where N is a power of 2) into a set of bit planes. This operation is useful for multiple problems. Certain modulation schemes assert data in bit-plane order as a simple means of analog-to-digital conversion. A Digital Light Processor based on the Texas Instruments' Digital Mirror Device uses this type of operation. In this context, the operation is sometimes referred to as corner turning. Certain image-coding schemes encode images in bit planes. These schemes would benefit from the planarized encoding. For 1-bit image data, this operation is equivalent to image transposition on N-bit wide tiles. This invention requires little modification to support this secondary use.
Bit-plane oriented schemes usually make poor use of memory bandwidth. To read a given bit position across an entire data set, prior art schemes read the entire data set, extract the bit of interest and discard the other bits. This process must be repeated for each bit plane. These prior art schemes read about N times as much data as actually used for N-bit data elements.
Traditional solutions to planarization can only effectively process one bit-plane at a time. The straight forward implementation reads the data N times. Even if all N bit planes are extracted the first time the data is read, the extraction process usually operates only one bit at a time.
Thus there is a need in the art for an efficient conversion process from pixel format data to bit plane format data. Such an efficient conversion process would make other processes feasible that are now limited by the computation cost of this planarization.